A light emitting diode (LED) is a solid state device that converts electrical energy to light. Light is emitted from active layers of semiconductor material sandwiched between oppositely doped layers when a voltage is applied across the doped layers. In order to use an LED chip, the chip is typically enclosed in a package that focuses the light and that protects the chip from being damaged. The LED package typically includes contact pads on the bottom for electrically connecting the LED package to an external circuit. Conventionally, an LED chip is designed to be packaged either as a discrete light emitter or with a group of LED chips in an array. The LED chip of the discrete light emitter is typically mounted on a carrier substrate, which in turn is mounted on a printed circuit board. The LED chips of the array, however, are typically mounted directed on the printed circuit board without using the carrier substrate.
Array products are not conventionally made using the discrete light emitters as building blocks. The carrier substrate of the discrete light emitter is typically considered needlessly to occupy space on the printed circuit board under an array. Moreover, conducting through-hole vias through the carrier substrate of the discrete light emitter would have to be reconfigured in order to connect properly to contact pads on the printed circuit board for each new array design. Thus, no carrier with a particular set of through-holes vias could be used as a standard building block. The problem of the through-hole vias in the discrete emitters can be solved by electrically connecting the LED chips to traces and contact pads on the top side of the carrier substrate. But eliminating the through-hole vias by connecting the LED chips to pads on the top side of the carrier substrate creates the new problem of how to connect the pads to a power source because the carrier substrate is no longer electrically coupled to the printed circuit board below.
FIG. 1 (prior art) shows an existing array product 10 with an array of twenty-six LED chips electrically connected to pads 11 on the top side of a carrier substrate 12. Array product 10 is the XLamp® MP-L EasyWhite product manufactured by Cree, Inc. of Durham, N.C. In FIG. 1, carrier substrate 12 is mounted on a metal disk 13 as opposed to on a printed circuit board. Carrier substrate 12 is attached to metal disk 13 using thermal glue 14. Array product 10 is inelegantly connected to power by hand soldering individual wires of the positive 15 and negative 16 power cord leads to the pads 11. Array product 10 has no features that facilitate connecting the pads 11 on the top side of carrier substrate 12 to a power source in the board or plate below. And array product 10 is not configured to be incorporated into a group of array products.
A method is sought for using one or more LED chips mounted on a carrier substrate as a standardized building block to make both a discrete light emitter as well as an array product of multiple substrates with mounted LEDs.